The present invention generally relates to metal polishing. In particular, it relates to planarizing copper and/or copper alloy metallization in manufacturing semiconductor devices.
Integrated circuits comprise a plurality of conductive patterns contained in or on layers of a silicon substrate. The conductive patterns include conductive lines, which are separated by dielectric material, and a plurality of interconnect lines. Conductive patterns on different layers are electrically connected by a conductive plug filling a via hole.
The conventional way of forming such conductive patterns has been to first blanket deposit a metal film onto the wafer surface and then etch the metal film using well known etching techniques to form the desired conductive pattern for that layer. Next, a dielectric film is deposited over the etched metal lines and vias are etched in the dielectric film to allow electrical connections for the next layer of metal that is to be deposited onto the dielectric film. This technique requires etching the metal and a deposition process with good gap fill capabilities for both the dielectric and metal layers.
An alternative interconnect fabrication technology, known as the damascene structure, has been developed in which no metal etching is required and in which the gap-filling capability is only required for the metal deposition processes and not for the dielectric deposition process. Metal etching and dielectric gap-fill are viewed as two of the semiconductor industry""s greatest challenges in moving to smaller dimension devices. Furthermore, copper, which is becoming the metal of choice for forming the conductive patterns in the next generation of integrated circuits, is notoriously difficult to etch. Accordingly, damascene technology is finding an increased amount of use by semiconductor manufacturers.
One particular method of damascene technology is dual damascene technology. In one approach to using dual damascene technology, an interlayer dielectric layer is deposited over a pattern and then subsequently planarized. Next, trench patterns that define the second conductive layer are formed in the dielectric using known photolithographic and etching techniques. After the trenches are etched, the resist layer used for the formation of the trenches is stripped and a second resist layer is deposited and patterned to define the openings or vias to the underlying conductive layer. The vias are etched, the second resist stripped and metal is deposited to fill the via and trenches. Where the conductive material is a metal, such as copper, the filling process is performed by blanket metal deposition. This deposition process provides excess conductive material on the surface of the dielectric layer that must be removed. Chemical mechanical polishing (CMP) is a typical method used for the removal.
In CMP, a polishing pad is brought into contact with a substrate containing excess material on the dielectric layer. The pad is moved relative to the substrate while pressure is applied against the backside of the substrate. A chemically reactive and oftentimes abrasive chemical composition is provided to the pad during polishing. The chemical composition reacts with the substrate and initiates the polishing process. Polishing is continued until the excess material on the surface is removed.
Various compositions have been proposed in the art for use in CMP. In one method that has been reported to be particularly useful for tungsten polishing, a slurry comprising an oxidizing agent, an abrasive and deionized water is used. The oxidizing agent is either copper sulfate or copper perchlorate, and the slurry pH is maintained between 4 and 6.
Another CMP composition discussed in the art is a slurry comprising an oxidizer, a catalyst and an abrasive in deionized water. The catalyst is typically chosen from metal compounds having multiple oxidation states (e.g. iron, copper and silver), with iron catalysts being preferred. A stabilizing compound can optionally be included in the slurry.
A CMP composition for planarizing metal surfaces, which includes a carboxylic acid, an oxidizing agent and water, has been discussed in the art. Examples of the oxidizing agent include hydrogen peroxide, nitric acid and derivatives of permanganic acid. The carboxylic acid (e.g., malic acid) typically has a molecular weight between 100 and 300. Alkali is used to adjust the composition pH to between 5 and 9. Optionally, the composition can include phosphoric acid and an abrasive.
In a reported method to polish copper, a chemical mechanical polishing composition comprising an oxidizer, an azole and a biodegradable detergent in deionized water or alcohol is used. The oxidizer is typically a compound such as nitric acid or hydrogen peroxide. Exemplary azoles include benzotriazole or its derivatives. The pH of the composition is usually adjusted to be in the 4 to 12 range.
A reported slurry for the chemical mechanical polishing of a copper, copper/tantalum or copper/tantalum nitride containing substrate includes an abrasive, an oxidizing agent, a complexing agent and an organic amino compound. The oxidizing agent is an inorganic or organic per-compound. Examples of complexing agents include organic acids such as citric acid and amino acids. Dodecylamine is an exemplary amino compound for the composition. The slurry can optionally contain a film forming agent, such as imidazole, and other additives, such as surfactants, stabilizers and dispersing agents.
While a number of CMP compositions have been discussed in the art, improved chemical compositions are always desirable, especially compositions that are useful for copper planarization.
The present invention provides a chemical mechanical polishing composition for planarizing copper and a method for planarizing, or initiating the planarization of, copper using the composition.
The chemical mechanical polishing composition includes an oxidizing agent and a copper (II) compound. The composition optionally includes one or more of the following compound types: a complexing agent; a corrosion inhibitor; an acid; and, an abrasive. In one embodiment, the oxidizing agent is hydrogen peroxide, ferric nitrate or an iodate. In another embodiment, the copper (II) compound is CuSO4.
The chemical mechanical polishing method involves the step of polishing a copper layer using a composition that includes an oxidizing agent and a copper (II) compound. The composition is formed in a variety of ways. In one embodiment, it is formed by adding the copper (II) compound to a solution containing the oxidizing agent, and any included optional compound types, in deionized water. In another embodiment, it is formed by adding a solution containing the copper (II) compound in deionized water to a solution containing the oxidizing agent, and any included optional compound types, in deionized water.
These and other embodiments of the present invention, as well as its features and some potential advantages are described in more detail in conjunction with the text below and attached figures.